Grease composition for constant velocity joints

ABSTRACT

Grease composition for constant velocity joints, comprising a base oil and a urea-based thickener, which grease additionally contains, (A) molybdenum sulphide dialkyldithiocarbamate and (B) 5,5-dithiobis(1,3,4-thiadiazole-2-thiol); a method of lubricating a constant velocity joint comprising packing it with said grease; and a constant velocity joint packed with said grease.

[0001] The present invention relates to a grease composition forconstant velocity joints, a method of lubricating a constant velocityjoint and to a constant velocity joint packed with a grease. Inparticular, the present invention relates to a grease composition whichcan be used for automobile drive shafts, propeller shafts and industrialmachinery joints.

[0002] Recent progress in mechanical technology has seen a growingdemand for the reduction in size and weight of machines, the enhancementof machine precision, the prolongation of machine life and so forth.

[0003] Constant velocity joints are special types of universal couplingswhich can transmit drive from the final reduction gear to a road wheelaxle at constant rotation velocity.

[0004] As the constant velocity joints used in automobiles andindustrial machines are used at high speeds and under high surfacepressure conditions, much better performance is demanded of the greaseused to lubricate these joints. This situation will be described in moredetail below with reference to constant velocity joints (herein belowabbreviated to CVJ) for automobiles.

[0005] With the promotion of front wheel drive cars and four wheel drivecars and the like, there has been a marked increase in the use of CVJ inthe automobile industry. Cars now have higher output and are smaller andlighter, which imposes severe demands on CVJ durability.

[0006] The grease used for CVJ lubrication is also subjected to thedemands for better joint durability and lifetime (damage resistance, forexample, flaking resistance and seizing resistance).

[0007] In response to these demands, sulphur-phosphorus-basedextreme-pressure agents comprising sulphurated fat/oil and/or olefinsulphide combined with zinc dithiophosphate, and lithium greasecomprising lead-based additives and molybdenum disulphide and the likehave mainly been used commercially. In recent years, urea grease, whichhas excellent heat resistance, has been used more than lithium grease.

[0008] Examples of prior art techniques which involve the use of amolybdenum sulphide dialkyldithiocarbamate include Japanese ExaminedPatent Application No. H4-34590 and Japanese Unexamined PatentApplication Nos. H6-57283, H6-330072 and H10-273692.

[0009] Japanese Examined Patent Publication No. H4-34590 discloses asystem comprising:—(A) molybdenum sulphide dialkyldithiocarbamate; and(B) at least one sulphur-phosphorus-based extreme pressure additivechosen from the group consisting of sulphurated fat/oil, olefinsulphide, tricresyl phosphate, trialkylthiophosphate and zincdialkyldithiophosphate, compounded into urea grease. However, suchsystems cannot always be said to be satisfactory under the currentsevere CVJ working conditions.

[0010] Japanese Unexamined Patent Application No. H6-57283 discloses asystem comprising molybdenum sulphide dialkyldithiocarbamate, molybdenumdisulphide and lead sulphide dialkyldithiocarbamate, compounded intourea grease. However, as this system contains a lead-based additive, itis undesirable in view of increasing concerns over environmentalprotection.

[0011] Japanese Unexamined Patent Application No. H6-330072 disclosesadding both (A) molybdenum sulphide dialkyldithiocarbamate and (C)triphenylphosphorothionate to urea grease, but these systems do notsimultaneously yield satisfactory damage resistance and abrasionresistance.

[0012] T. Sakurai's “Sekiyu Seihin Tenkazai” [Petroleum ProductAdditives] (p. 262 and thereafter) introduces thiadiazole compounds aslubricant oil additives, and Table 3 on p. 226 suggests that theaddition of thiadiazole-based compounds results in excellentsulphuration corrosion prevention with respect to copper and silver.Moreover, Japanese Examined Patent publication No. H4-32880 disclosesimproved load resistance and extreme pressure properties withoutcorrosion or discoloration of the metal as a result of adding5,5′-dithiobis(1,3,4-thiadiazole-2-thiol) to lubricating grease, but nomention is made of the problem of balancing damage resistance andabrasion resistance.

[0013] Japanese Unexamined Patent Application No. H11-131086 disclosesthe use of a thiadiazole-based compound as an additive in lubricatinggrease obtained using a calcium sulphonate complex-based thickeningagent, but the thiadiazole-based compound is used here to deactivatemetals.

[0014] Japanese Unexamined Patent Application No. H10-273692 discloses agrease composition for constant velocity joints comprising diurea asthickener, wherein molybdenum disulphide, phosphorus-free sulphur-basedextreme pressure additive and sulphur-nitrogen-based extreme pressureadditive are used in combination with (A) molybdenum sulphidedialkyldithiocarbamate. However, it is not clear which specificcompounds can be used as the sulphur-nitrogen-based extreme-pressureagent, as “Vanlube 601” (trademark), manufactured by R. T. Vanderbilt,is merely disclosed in the working examples, and said trade name merelyconfirms that “Vanlube 601” is a heterocyclic sulphur-nitrogen compound.Moreover, according to this technique, the combined use of molybdenumdisulphide and phosphorus-free sulphur-based extreme pressure additiveis indispensable.

[0015] EP-A-0633 304 discloses a urea grease composition comprising aurea grease and, incorporated therein as additives, a sulfurizedmolybdenum dialkyldithiocarbamate represented by formula (A):—

(R₁R₂N—CS—S)₂—Mo₂O_(m)S_(n)

[0016] wherein R₁, and R₂ each independently represent an alkyl grouphaving from 1 to 24 carbon atoms, m+n=4, m is 0 to 3, and n is 4 to 1,and triphenylphosphorothionate (B).

[0017] There is a demand for both satisfactory damage resistance andsatisfactory abrasion resistance in the field of lubricating greasecompositions for constant velocity joints. There are many greases whichhave good abrasion resistance but poor damage resistance. There isconsiderable demand for the discovery of a grease composition forconstant velocity joints which provides improvement in both of thesephysical properties.

[0018] It has now been found possible to formulate greases for constantvelocity joints containing 5,5′-dithiobis(1,3,4-thiadiazole-2-thiol),having advantageous properties with regard to damage resistance andabrasion resistance.

[0019] The present invention provides a grease composition for constantvelocity joints comprising a base oil and a urea-based thickener, whichgrease additionally contains, (A) molybdenum sulphidedialkyldithiocarbamate; and (B)5,5′-dithiobis(1,3,4-thiadiazole-2-thiol).

[0020] In a preferred embodiment, the grease composition of the presentinvention further contains, (C) triphenylphosphorothionate.

[0021] The molybdenum sulphide dialkyldithiocarbamate (A) mayconveniently be a compound represented by general formula (1) below:—

(R¹R²N—CS—S)₂—Mo₂O_(m)S_(n)  (1)

[0022] wherein R¹ and R² are groups independently chosen from the groupconsisting of alkyl groups of from 1 to 24 carbon atoms, m+n=4, m isfrom 0 to 3 and n is from 1 to 4.

[0023] Preferred alkyl groups are those having from 1 to 18 carbonatoms, more preferably from 1 to 12 carbon atoms, even more preferablyfrom 1 to 6 carbon atoms and most preferably from 1 to 4 carbon atoms.Said alkyl groups maybe linear or branched.

[0024] Specific examples of molybdenum sulphide dialkyldithiocarbamate(A) that may be conveniently used in the present invention include oneor more of molybdenum sulphide diethyldithiocarbamate, molybdenumsulphide dibutyldithiocarbamate, molybdenum sulphidediisobutyldithiocarbamate, molybdenum sulphidedi(2-ethylhexyl)dithiocarbamate, molybdenum sulphidediamyldithiocarbamate, molybdenum sulphide diisoamyldithiocarbamate,molybdenum sulphide dilauryldithiocarbamate, molybdenum sulphidedistearyldithiocarbamate, molybdenum sulphiden-butyl-2-ethylhexyldithiocarbamate and molybdenum sulphide2-ethylhexylstearyldithiocarbamate.

[0025] 5,5′-dithiobis(1,3,4-thiadiazole-2-thiol) (B) may be representedby formula (2) below:—

[0026] Preferred compositions according to the invention have one ormore of the following features:

[0027] (i) from 0.5 to 10% by weight of A;

[0028] (ii) from 0.5 to 5% by weight of A;

[0029] (iii) at least 2% by weight of A;

[0030] (iv) up to 3% by weight of A;

[0031] (v) from 0.1 to 10% by weight of B;

[0032] (vi) from 0.1 to 5% by weight of B;

[0033] (vii) at least 0.5% by weight of B, and

[0034] (viii) up to 2% by weight of B, with respect to the total weightof the grease composition.

[0035] Particularly preferred compositions according to the inventionare those having features (i) and (v); those having features (i) and(vi); those having features (i) and (vii); those having features (i) and(viii); those having features (i), (vii) and (viii); those havingfeatures (ii) and (v); those having features (ii) and (vi); those havingfeatures (ii) and (vii); those having features (ii) and (viii); thosehaving features (ii), (vii) and (viii); those having features (iii) and(v); those having features (iii) and (vi); those having features (iii)and (vii); those having features (iii) and (viii); those having features(iii), (vii) and (viii); those having features (iv) and (v); thosehaving features (iv) and (vi); those having features (iv) and (vii);those having features (iv) and (viii); those having features (iv), (vii)and (viii); those having features (iii), (iv) and (v); those havingfeatures (iii), (iv) and (vi); those having features (iii), (iv) and(vii); those having features (iii), (iv) and (viii); and those havingfeatures (iii), (iv), (vii) and (viii).

[0036] If less than 0.5% by weight of A is used, a reduced effect on theCVJ damage resistance is achieved, whereas there is no incentive to usemore than 10% by weight of A, as above this concentration limited or nofurther improvement can be expected.

[0037] If less than 0.1% by weight of B is used, a reduced effect on theCVJ damage resistance is achieved, whereas there is no incentive to usemore than 10% by weight of B, as above this concentration limited or nofurther improvement can be expected.

[0038] The triphenylphosphorothionate (C) is a compound represented byformula (3) below:—

(C₆H₅—O)₃—P═S  (3)

[0039] When triphenylphosphorothionate (C) is added, it is preferablyincorporated in a concentration of up to 10% by weight, e.g., from 0.1to 10% by weight, more preferably from 0.1 to 5% by weight, with respectto the total weight of the grease composition.

[0040] If less than 0.1% by weight of C is added, a reduced effect onthe abrasion resistance is achieved, whereas there is no incentive touse more than 10% by weight of C, as above this concentration limited orno further improvement can be expected.

[0041] Any urea-based thickener can be used as the urea compound usedfor the thickener, and there are no particular limitations on the typethereof. For example, diurea, triurea and/or tetraurea may beconveniently used. Mineral oil and/or synthetic oil is used as the baseoil. In a preferred embodiment of the present invention, from 2 to 35%by weight of urea-based thickener is used with respect to the totalweight of the grease composition.

[0042] It is also possible to add various additives such asantioxidants, rust preventers and extreme-pressure agents to the greasecomposition of the present invention.

[0043] Preferred lubricating grease compositions for constant velocityjoints according to the invention specifically described herein haveconsiderably improved flaking resistance and seizing resistance (damageresistance) and also have excellent abrasion resistance andtemperature-control properties.

[0044] The present invention will now be described with reference to thefollowing examples, which are not intended to limit the scope of thepresent invention in any way.

EXAMPLES

[0045] Preparation of Grease Compositions

[0046] Additives were added to base grease according to the formulationsshown in Tables 1 to 3, and the resulting systems were treated using a3-roller mill to yield grease for the Working Examples and ComparativeExamples. It should be noted that purified mineral oil having akinematic viscosity of 15 mm²/s at 100° C. was used as the base oil.

[0047] I Diurea Grease

[0048] 1 mol of diphenylmethane-4,4′-diisocyanate and 2 mol ofoctylamine were reacted in base oil, and the resulting urea compound wasuniformly dispersed to yield base grease. The urea compound content wasset at 10% by weight.

[0049] II Tetraurea Grease

[0050] 2 mol of diphenylmethane-4,4′-diisocyanate, 2 mol of octylamineand 1 mol of ethylene diamine were reacted in base oil and the resultingurea compound was dispersed uniformly to yield base grease. The ureacompound content was set at 15% by weight.

[0051] The thickness, abrasion resistance, joint damage and jointdurability shown in the accompanying tables were appraised according tothe following test methods.

[0052] (1) Thickness was appraised according to JIS K2220 5.3

[0053] (2) Abrasion resistance was appraised according to ASTM D2266.

[0054] (3) Joint damage test

[0055] Each sample was introduced into a commercial CVJ and the systemwas operated under the following conditions, then the presence orabsence of the fine damage that is a sign of flaking inside the jointwas appraised, and the maximum temperature of the joint during theoperation was also appraised.

[0056] CVJ type: Barfield joint

[0057] rpm: 1500 rpm

[0058] Joint angle: 8°

[0059] Torque: 300 N.m

[0060] Time: 1 hour

[0061] Appraisal: (◯) no damage; x damage; Δ slight damage

[0062] (4) Joint durability test

[0063] Each sample was introduced into a commercial CVJ and the systemwas operated under the following conditions, then the presence orabsence of flaking or seizure of the ball in the joint or of the innerrace, outer race or cage was appraised.

[0064] CVJ type: Barfield joint

[0065] rpm: 1500 rpm

[0066] Joint angle: 8°

[0067] Torque: 300 N.m

[0068] Time: 150 hours

[0069] Appraisal: (◯) no damage; Δ slight flaking; x flaking (continueduse impossible) TABLE 1 Working Working Working Example Example Example1 2 3 Base grease Diurea grease 95.0 95.0 — (% wt) Tetraurea grease — —95.0 Additives A-1 *1 3.0 2.0 — (% wt) A-2 *2 — — 2.0 B *3 2.0 0.5 0.5 C*4 — 1.0 1.0 Test results Thickness 60 W 320 316 318 Abrasion 0.47 0.400.39 resistance (mm) Joint damage (O) (O) (O) test Joint 128 101 108temperature (° C.) Joint durability (O) (O) — test

[0070] TABLE 2 Compara- Compara- Compara- tive tive tive Example ExampleExample 1 2 3 Base grease Diurea grease 92.0 96.0 98.0 (% wt) Tetraureagrease — — — Additives A-1 *1 3.0 3.0 — (% wt) A-2 *2 — — — B *3 — — 2.0C *4 1.0 1.0 2,5-bis (tert- 4.0 — — octyldithio)- 1,3,4-thiadiazole Zincdialkyl — — — dithiophosphate Molybdenum — — — disulphide Test Thickness60 W 312 326 321 results Abrasion 0.45 0.39 0.55 resistance (mm) Jointdamage test Δ x x Joint temperature 120 107 154 (° C.) Joint durabilityΔ x — test

[0071] TABLE 3 Compara- Compara- Compara- tive tive tive Example ExampleExample 4 5 6 Base grease Diurea grease 96.0 96.0 92.0 (% wt) Tetraureagrease — — — Additives A-1 *1 — 3.0 3.0 (% wt) A-2 *2 — — — B *3 1.0 — —C *4 1.0 — — 2,5-bis (tert- 2.0 — — octyldithio)- 1,3,4-thiadiazole Zincdialkyl — 1.0 — dithiophosphate Molybdenum — — 5.0 disulphide TestThickness 60 W 322 318 316 results Abrasion 0.48 0.41 0.65 resistance(mm) Joint damage test x x x Joint temperature 106 108 118 (° C.) Jointdurability — x — test

1. Grease composition for constant velocity joints, comprising a baseoil and a urea-based thickener, which grease additionally contains, (A)molybdenum sulphide dialkyldithiocarbamate and (B)5,5′-dithiobis(1,3,4-thiadiazole-2-thiol).
 2. Grease compositionaccording to claim 1, containing from 0.5 to 10% by weight of (A)molybdenum sulphide dialkyldithiocarbamate and from 0.1 to 10% by weightof (B) 5,5′-dithiobis(1,3,4-thiadiazole-2-thiol), with respect to thetotal weight of grease composition.
 3. Grease composition according toclaim 1 or 2, wherein said grease contains from 0.5 to 5% by weight of(A) molybdenum sulphide dialkyldithiocarbamate and 0.1 to 5% by weightof (B) 5,5′-dithiobis(1,3,4-thiadizole-2-thiol), with respect to thetotal weight of grease composition.
 4. Grease composition according toany one of claims 1-3, wherein said grease contains from 2 to 35% byweight of urea-based thickener, with respect to the total weight of thegrease composition.
 5. Grease composition according to any one of claims1-4, wherein (A) molybdenum sulphide dialkyldithiocarbamate is selectedfrom one or more of molybdenum sulphide diethyldithiocarbamate,molybdenum sulphide dibutyldithiocarbamate, molybdenum sulphidediisobutyldithiocarbamate, molybdenum sulphidedi(2-ethylhexyl)dithiocarbamate, molybdenum sulphidediamyldithiocarbamate, molybdenum sulphide diisoamyldithiocarbamate,molybdenum sulphide dilauryldithiocarbamate, molybdenum sulphidedistearyldithiocarbamate, molybdenum sulphiden-butyl-2-ethylhexyldithiocarbamate and molybdenum sulphide2-ethylhexylstearyldithiocarbamate.
 6. Grease composition according toany one of claims 1-5, which further contains, (C)triphenylphosphorothionate.
 7. Grease composition for according to claim6, containing from 0.1 to 10% by weight of (C)triphenylphosphorothionate, with respect to the total weight of greasecomposition.
 8. Grease composition according to claim 6 or 7, whereinsaid grease contains from 0.1 to 5% by weight of (C)triphenylphosphorothionate, with respect to the total weight of greasecomposition.
 9. A method of lubricating a constant velocity jointcomprising packing it with a grease according to any one of claims 1 to8.
 10. A constant velocity joint packed with a grease according to anyone of claims 1 to 8.